France centre Gael Fickou praised his team's defence after Saturday's 23-10 home win over La Rochelle to send them to the summit of the French Top 14.
Fickou, 27, created the crucial second-half try after the Parisians had held out in the opening 40 minutes, with the away side controlling territory and possession.
Fickou, who arrived in March after a controversial move from local rivals Stade Francais, left the field to applause from his new home crowd as Racing gained revenge for June's play-off defeat.
"We won thanks to our state of mind. Defensively we were sound against a very good La Rochelle team. It's never easy to face them," Fickou told broadcaster Canal+.
"We put in a physical challenge, compared to last season's semi-final when we weren't quite there. Tonight, we rose to the level."
The visitors' director of rugby Ronan O'Gara was forced into three changes from last Sunday's opening weekend loss to champions Toulouse with Australia lock Will Skelton banned pending a disciplinary hearing for a shoulder charge.
At La Defense Arena, the hosts led 7-3 at the break as Fickou's club and Test midfield partner Virimi Vakatawa crossed following a delicate Kurtley Beale pass between the Australia full-back's legs.
The sides were level 10-10 going into the final quarter as Kevin Gourdon charged over for La Rochelle.
Fickou's moment of individual brilliance came with 10 minutes to go as he broke free 40m out and was only stopped as Remi Bourdeau dived on the centre as he was about to ground the ball to score.
Referee Tual Trainini showed Bourdeau a yellow card and awarded a penalty try following the efforts from Fickou, who also made a leading 14 tackles as Racing held on for the victory.
- Car-lifting Castres -
Earlier, former New Zealand sevens winger Ben Lam opened his account for the new season as Bordeaux-Begles beat Stade Francais 37-10 with a bonus point.
Les Bleus' fly-half Matthieu Jalibert impressed by kicking 15 points and set up Samoa centre UJ Seuteni with a sublime off-load but was shown a first-half yellow card for an intentional knock-on.
French back-rower Kevin Kornath crashed over in the 77th minute as Castres overcame Clermont 34-30 to go top of the table.
Earlier in the day Castres players were filmed lifting and moving a car on their way to the stadium as it had blocked their team bus.
"It's an incredible end to the game, the solidarity perfectly reflects our team spirit," Castres' veteran lock Loic Jacquet told Canal+.
"It confirms not just the work since the start of this season, but the work carried over from last season. It's great. Two wins from two is brilliant."
On Sunday, champions Toulouse host Toulon, who are set to hand Fiji's Olympic gold medallist Jiuta Wainiqolo a debut as English 21-year-old Harrison Obatoyinbo starts his first Top 14 game on the opposite wing.
The home side's flanker Anthony Jelonch, who captained France during July's series loss to the Wallabies, is named on the bench for his new club after moving from Castres during the summer.